what triggered tamerlan's cad ralization? luis vasquez who befriended him said he last saw tamerlan three years ago. when i asked why his friend drifted to radical islam -- >> the only thing i can think of, i only want to say what i'm sure of, that one of the sources of this could have been some kind of dissatisfaction of the bad, slow transition to coming to another country from a different one, as a teenager. that's never easy. >> vasquez now shares the sentments of those at the mosque, perplexed as to why the man they knew drifted in that direction, and angry he did it. >> lots of unanswered questions. brian todd, thanks very much. >>> one bostonian that was uncomfortably close to tsarnaev's gun fight with the police tells his story to cnn. a bullet went right through his roommate's desk chair. >>> plus, another dramatic cnn interview with the mother of the bombing suspects, who insists they were framed. [ male announcer ] if she keeps serving up sneezes... [ sneezing ] she may be muddling through allergies. try zyrtec®.